You can get some good info on an instructor by going to their profile page in a course. Just go to People and click on their name. On the right you'll see two options: a Student Interaction Report, and an Access Report.

You can also separately track how they did grading by going to the Gradebook, clicking the gear icon in the upper right corner, and selecting "View Gradebook History." You can see how quickly they are entering grades, what grade changes they've made, etc.

There is apparently a User Access Report (this is different than the Last User Access Report) that was developed by Instructure Professional Services and can be turned on for a fee by your CSM. I would recommend contacting your CSM for more information about that report. The other option is to look at a vendor like AspireEDU.